1. Field of the Invention
The present invention relates to a coating film and a member provided with the coating film, and to a method of producing the coating film. More particularly, the present invention is directed to a coating film, which is not likely to cause cracks as a result of relief of stress caused by a difference in thermal expansion coefficient with the base or deformation, and also has improved resistance of the coated surface, especially oxidation resistance, corrosion resistance and gas permeation resistance, a member provided with the coating film, and a method of producing the coating film.
2. Background Technology
In processes of manufacturing semiconductor devices such as IC, LSI, VLSI, et al, various semiconductor manufacturing apparatuses have hitherto been used to carry out various processes, for example, heating processes, etching processes, oxidation processes, film forming processes (using CVD, PVD, or plasma CVD processes), sputtering processes, and ion implantation processes.
In these semiconductor manufacturing apparatuses, corrosive gases and corrosive liquids are frequently used in the manufacturing processes. Therefore, a metal member to be contacted with these corrosive substances is likely to be corroded, causing not only particulate contaminants to be generated, but also contamination of the apparatus due to metal impurities contained in the metal member, and thus defects in semiconductor wafers are likely to be caused by this contamination. For example, since corrosive gases such as hydrogen chloride and hydrogen bromide gases are used in a dry etching process, it was necessary to use a material having corrosion resistance as a material for the metal member, such as iron and aluminum, used in the etching system.
As the metal material of the semiconductor manufacturing apparatus, stainless steel is used in place of iron which has conventionally been used. Alternatively, the surface of stainless steel is electropolished and a passive film (Cr2O3) is further formed thereon. SUS316L having excellent corrosion resistance among stainless steels is also used; however, it does not always have satisfactory corrosion resistance in the environment of semiconductor manufacturing apparatuses.
Although the surface thereof is also coated with a fluororesin, the film coated with the fluororesin contains a trace amount of metal impurities, thereby causing contamination with impurities. Furthermore, the fluororesin could not be applied to the semiconductor manufacturing apparatus for processing at high temperatures higher than the temperature at which the fluororesin can withstand because the service temperature of the fluororesin is limited.
With respect to the portion where aluminum is used as the metal material of the semiconductor manufacturing apparatus, a trial of anodizing the surface was also made to enhance the surface corrosion resistance. However, since a large number of micropores exist on the surface of the anodized aluminum member, raw gases are adsorbed into the micropores and are then released in subsequent steps, and thus a deleterious influence is likely to be exerted in the subsequent steps. Micropores on the surface make it difficult to wash out stains, thereby causing contamination with impurities.
As the method for rust prevention of the metal used under high-temperature conditions, for example, a trial of improving the high-temperature corrosion resistance by coating the surface of the metal member with a thermal decomposition product of polysilazane was also made (Japanese Patent Application, First Publication No. Hei 5-345983).
According to this method, a metal member is coated with a film having excellent corrosion resistance or a film having excellent high-temperature oxidation resistance by coating the surface of the metal member with perhydropolysilazane or polyorganosilazane and heating to 100 to 600xc2x0 C., thereby converting perhydropolysilazane or polyorganosilazane into a silica glass film.
A dense coating film can be obtained by coating the surface of the metal member with perhydropolysilazane and heat treating it in air. A flexible coating film can be obtained by coating the surface of the metal member with polyorganosilazane and heat treating it in air.
In addition, since a simple substance of perhydropolysilazane or polyorganosilazane is coated in the form of a single layer in the method of coating the surface of the metal member with the thermal decomposition product of polysilazane, a coating film which is both dense and flexible was difficult to obtain, although a dense coating film or a flexible coating film can be obtained.
In the case of a stainless steel chamber, a coating film containing silicon dioxide as a principal component is formed on the inner surface of the chamber by coating the inner surface of the chamber with perhydropolysilazane and heat treating it in air to impart the oxidation resistance to the inner surface. To cover the unevenness of the inner surface and to improve the oxidation resistance, it is necessary to form a coating film which is as dense as possible and is also thick.
However, if the thickness of the coating film is increased, films overlap with each other or a coating solution is accumulated, and thus the resulting coating film has a local thick portion, and defects such as cracks and deformation are likely to occur during the following heat treatment. The thickness of the coating film must be entirely reduced and is limited to about 1.5 to 2 xcexcm at most.
The film obtained from perhydropolysilazane is a film which is dense and has excellent corrosion resistance. In the case of coating the surface of the metal such as stainless steel with perhydropolysilazane and heat treating, a difference in the thermal expansion coefficient between the film that was obtained by heat treating the perhydropolysilazane and the metal as a raw material causes stress in the film, and thus defects such as pinholes, cracks and microcracks are likely to occur.
In the case in which the surface of the metal includes defects such as sharp scratches, pinholes and deep irregularities, the surface of the metal cannot be covered if the thickness of the coating film is not increased. However, when the thickness is increased, defects such as pinholes, cracks, and microcracks occur in the film as compared with the case in which the film is thin. As described above, defects in the film promote corrosion in the metal provided with the coating film, resulting in poor corrosion resistance.
To eliminate the defects in the film, the film may be made thin. If the film is made thin, it becomes impossible to completely cover the surface of the metal, resulting in poor corrosion resistance.
Furthermore, it is difficult to form the preheat-treatment coating film at acutely angled portions of the metal member, for example, at the end faces and sharply scratched portions, and to form a uniform silica glass film.
The silica glass film using known polysilazane was an insufficient countermeasure for preventing the corrosion when used under such severe conditions as a high-temperature corrosive atmosphere like in the semiconductor manufacturing apparatuses.
The present invention has been made to solve the problems described above, and an object of the present invention is to provide a coating film, which is not likely to cause cracks and is also capable of improving the resistance of the coated surface, especially oxidation resistance, corrosion resistance and gas permeation resistance, a member provided with the coating film, and a method of producing the coating film.
To solve the problems described above, a coating film and a member provided with the same, and a method of producing the coating film were employed in the present invention.
The coating film of the present invention comprises: a dense layer containing silicon dioxide as a principal component, which is obtained by heat-treating a solution containing perhydropolysilazane and polyorganosilazane, a ratio of the content of perhydropolysilazane to the total amount of polysilazane including perhydropolysilazane and polyorganosilazane being from 0.65 to 0.95.
According to this coating film, it becomes possible to prevent cracks from occurring at the surface of the base and to prevent oxidation due to a high-concentration acidic substance. In addition to the oxidation resistance, the corrosion resistance and gas permeation resistance can also be improved.
The coating film may further comprise a second layer containing silicon dioxide as a principal component formed on the dense layer, the second layer being obtained by heat-treating a second solution containing perhydropolysilazane and polyorganosilazane, the content of polyorganosilazane being greater than that of the solution.
Another coating film of the present invention is a coating film formed on at least a portion of a base, comprising: a dense layer containing silicon dioxide as a principal component, which is obtained by heat-treating a solution containing perhydropolysilazane and polyorganosilazane, a ratio of the content of perhydropolysilazane to the total amount of polysilazane including perhydropolysilazane and polyorganosilazane being from 0.95 to 1.0; and a second layer containing silicon dioxide as a principal component formed on the dense layer, the second layer being obtained by heat-treating a second solution containing perhydropolysilazane and polyorganosilazane, the content of polyorganosilazane being larger than that of the solution.
According to this coating film, since the second layer is formed on the dense layer, cracks in the dense layer can be prevented from occurring. Since the surface of the base was coated with the dense layer, oxidation due to a high-concentration acidic substance can be prevented. In addition to the oxidation resistance, the corrosion resistance and gas permeation resistance can also be improved.
The coating film may further comprise a third layer containing silicon dioxide as a principal component formed on the second layer, the third layer being obtained by heat-treating a third solution containing perhydropolysilazane and polyorganosilazane, the content of polyorganosilazane being less than that of the second layer.
Still another coating film of the present invention is a coating film formed on at least a portion of a base, comprising: a flexible layer containing silicon dioxide as a principal component, which is obtained by heat-treating a solution containing perhydropolysilazane and polyorganosilazane, a ratio of the content of perhydropolysilazane to the total amount of polysilazane including perhydropolysilazane and polyorganosilazane being from 0 to 0.65; and a second layer containing silicon dioxide as a principal component formed on the flexible layer, the second layer being obtained by heat-treating a second solution containing perhydropolysilazane and polyorganosilazane, the content of polyorganosilazane being less than that of the solution.
According to this coating film, it is made possible to impart flexibility to the coating film and to relieve stress caused by a difference in thermal expansion coefficient with the base or deformation. Since the flexible layer can be made thicker, stress can be relieved more effectively.
The flexible layer and/or the second layer may comprise a laminate of plural layers containing silicon dioxide as a principal component obtained by separately heat-treating plural solutions having different contents of polyorganosilazane.
The coating film may further comprise an adhesion improved layer formed between the base and the flexible layer.
The member of the present invention is a member made of metal, ceramic, or a synthetic resin, comprising the coating film of the present invention formed on at least a portion of the surface thereof.
According to this member, it is made possible to prevent cracks from occurring at the surface of the member and to prevent oxidation of the member due to a high-concentration acidic substance. In addition to the oxidation resistance, the corrosion resistance and gas permeation resistance can also be improved.
The method of producing a coating film of the present invention comprises: coating at least a portion of the surface of a base with a solution containing perhydropolysilazane and polyorganosilazane, each content being adjusted to a predetermined value, and heat-treating the solution in air or air containing water vapor to form a dense or flexible layer containing silicon dioxide as a principal component.
According to this method, it becomes possible to easily form a coating film on at least a portion of the surface of the base without a fear of cracks and a fear of oxidation due to a high-concentration acidic substance, and without using a special apparatus. Also, it becomes possible to reduce the cost of the resulting product because the apparatus is relatively inexpensive and the processes simple.
As described above, the present invention can provide a coating film which is not likely to cause cracks in the coated surface and is also capable of improving the resistance of the coated surface, especially oxidation resistance, corrosion resistance, and gas permeation resistance.
Also, the present invention can provide a member made of metal, ceramic, or a synthetic resin, provided with the coating film.
Also, the present invention can provide a method of producing the coating film, and is capable of easily forming the coating film of the present invention without using a special apparatus, reducing the cost of the resulting product.